The Presbyterian Church has written to all members of the legislative assembly of Northern Ireland (MLAs) stating its opposition to marriage equality.

The Northren Ireland assembly at Stormont is due to vote today a motion tabled by the Sinn Fein party that calls upon legislators to introduce same-sex marriage legislation.

The motion states that assembly ‘believes that all couples, including same-sex, should have the right to marry in the eyes of the state, while the rights of religious institutions to define, observe and practise marriage within their beliefs should be given legal protection.

‘That all married couples, including those of the same sex, should have the same legal entitlement to the protections, responsibilities, rights, obligations and benefits afforded by the legal institution of marriage.

‘Calls on the minister of finance and personnel to introduce legislation to guarantee that couples of any sex or gender identity receive equal benefit.

‘Further calls on the first minister and deputy first minister to ensure that all legislation adheres to the government's commitments to protect equality for all’.

In the letter, the Presbyterian Church has urged the assembly not to ‘demolish a fundamental building block of society’ by voting in support of gay marriage at Stormont today.

Since 2005 it has been possible to enter into a civil partnership across the United Kingdom. Today’s motion — also strongly opposed by the DUP — calls for same sex couples in Northern Ireland to be entitled to have their marriage recognised in the eyes of the law.

The Church’s letter was sent from the Presbyterian General Assembly’s church and society committee. It is signed by its co-convenor Dr Norman Hamilton, a former Moderator.

It stated that the issue is ‘not merely an issue of conscience for Christian people and Christian churches, but a very significant one for the whole of society.

‘… effectively demolish generations and centuries of societal norms established on Judaeo-Christian values. The steady erosion of such values, with minimal debate about the world view replacing them, causes us the very greatest concern.

‘We would however contend that this is not in fact an issue of equality, as all of the significant legal benefits and rights available through marriage are already available through civil partnership.

‘It would be entirely inappropriate to demolish a fundamental building block of society, such as the historic view of marriage, when such a step is not actually necessary.’

Green Party MLA Steven Agnew told the BBC the motion was ‘simply about equality.

‘As the law stands at the moment, a couple without faith can get married in a church while a devoutly religious couple of the same sex cannot.

‘Whether a religious institution performs same-sex marriage ceremonies is a matter for the church involved, not the state.

‘This is actually an extension of rights to religious institutions to make their own decisions on this issue.

‘Therefore, the law preventing churches performing same-sex marriage ceremonies should be removed and instead legal protection should be given to churches to allow then to determine what they define as marriage.’

Sinn Fein said that marriage equality is ‘a human rights issue’.

The party’s equality spokesperson, Bronwyn McGahan, told the daily Belfast Telegraph : ‘Every citizen should enjoy the same rights under State law and that includes those in relation to marriage.

‘What churches do is a matter for churches, but the State needs to treat everyone with equality. There have been a succession of similar motions and these are being brought forward because this is a human rights and equality issue.

‘LGBT couples should have the same rights as any other citizen on this island’.

The DUP is firmly opposed to any legislation for marriage equality.

While Stormont currently has no plans for such legislation, local parties have been formulating policies on the issue.

Westminster is consulting on whether to allow gay couples in England and Wales to marry, while in Scotland the SNP government has announced plans to bring forward a bill on the issue.